The administration of antigenic material to produce immunity, or close to immunity, to a disease.

Only people in third world countries who can't afford it and retarded people who either don't understand science or are religious nutjobs don't get vaccines. Some wackos still think it causes like autism - but there is absolutely no link between the two and these people are both wrong and doing damage to the research that could be getting done on the real reasons for autism.

The two rounds of vaccinations have eradicated polio from most of the countries in the world and reduced the worldwide incidence from an estimated 350,000 cases in 1988 to just over 1000 cases in 2007.